A. Field of the Invention
The present invention relates generally to the field of gasketing products, compositions and methods, especially to the field of hot-melt, formed-in-place compositions flowed onto containers such as drums and pails made of metal, fiber or plastic.
B. Prior Art
Currently, to provide suitable sealed closures for drums and pails or the like, it is the usual practice to employ conventional plastisol or rubber latex materials. The latter materials require considerable energy (heat) first to remove water from the compositions while they are being prepared and then again when the compositions are cured to form the gasket. Gaskets have also been formed by applying liquid plastisol compositions directly onto lids or closures at room temperature. The lids are then put into an oven at a temperature of about 420.degree. F. for about four minutes. Then, to effect post-cure, they are again subjected to high temperature conditions for a considerable length of time which entails very large energy usage. Both of the last two steps result in heating the lids to hard-to-handle temperatures.
Conventionally, it is also known to provide or insert a previously-formed gasket as a separate item between the open end of the container and its lid or cover. In some instances, the previously-formed gasket is secured to the lid or cover by the use of a suitable adhesive material that is compatible with the gasket material and with the contents stored in the container.
Conventional gaskets often do not have the desirable qualities of the gasket products of the present invention. One quality that is often lacking is high resistance to compression set. This means that the containers presumably closed by such conventional gaskets may in fact be highly susceptible to leaks through the gasket under certain conditions.
Typical gasketing materials that have been employed in the past with varying degrees of success include soft metal such as copper, and numerous resilient non-metallic products including cork, rubber, neoprene and other plastic materials. Such materials have included fluorocarbon polymers, plasticized vinyls, silicone and thermoplastic elastomers.
It is therefore among the objects of the present invention to provide a superior gasket product which:
1. Has excellent slip and flexibility characteristics.
2. Is resistant to exudation of its constituent components such as plasticizing oils or the like.
3. Has high resistance to compression set.
4. Is made of relatively low cost materials.
5. May be made in a relatively low cost process.
6. Is sparing of heat usage during its fabrication.
7. Can be made in a hot-melt application directly onto the container lid in a short time.
8. Does not require any adhesives to keep it in place relative to the closure of the container, yet is relatively easy to remove therefrom.
9. Has high resistance to water-soluble materials.
It is also among the objects of the invention to provide:
10. A process for forming gaskets by flowing a fluid having good viscoelastic properties onto the closure of the drum, pail or other container.
11. A process for forming a gasket in which curing of the gasket composition is effected substantially simultaneously with the application of the composition to the closure of the container.
12. A process which minimizes the need for long periods of post-curing at quite high temperatures.